1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Laser scanning systems and LED exposure systems have been popularized as the image writing systems (exposure systems) among the conventional image forming apparatuses such as copying machines and printers. LED exposure system is a system for forming a latent image on the surface of a photosensitive drum by exposing, using the imaging means, the surface of the photoreceptor to light emitted from an exposure device having a plurality of light-emitting elements lined up along the axial direction of the photosensitive drum. For the reason of the light intensity, the LED exposure system needs to have the exposure device placed close to the photosensitive drum, requiring high precision in the positional relation between the exposure device and the photosensitive drum.
In light of this fact, there has been known a configuration in which an LED unit is provided with a positioning portion (a roller), which is brought into contact with a predetermined contact portion to keep the distance between the LED head (exposure unit) of the LED unit and the photosensitive drum constant at the time of image formation (see Japanese Patent Application Laid-open No. 2009-210613). There is also known a method for packaging the process cartridges in an image forming apparatus main body to transport the image forming apparatus along with the process cartridges (see Japanese Patent Application Laid-open No. H7-104637).
When transporting an image forming apparatus in which a positioning portion for positioning an LED head (an exposure unit) in relation to a photosensitive drum (a photoreceptor) is in contact with a predetermined contact portion, the surface of the positioning portion or the predetermined contact portion could be damaged by, for example, vibration of the transportation. The damaged surface of the positioning portion could inhibit accurate positioning of the LED head with respect to the photosensitive drum at the time of image formation and therefore affect the image formation.
In view of the foregoing problems, an object of the present invention is to prevent damage to the positioning portion for positioning the exposure unit with respect to the photoreceptor at the time of image formation or to the predetermined contact portion.